In order to ensure their safe operation, nuclear power plants are subject to very stringent safety regulations and inspections. These plants are periodically inspected in order to ensure their proper operation and to protect plant workers and the environment from the hazardous effects of leakage of radioactive material. As part of this routine inspection program, the steam generators of nuclear power plants are regularly inspected for leakage in the heat exchanger tubes and for tubes which are potentially defective. This inspection is usually accomplished by means of remotely controlled eddy current testing apparatus. As defective tubes are discovered by means of the eddy current testing apparatus, their position is noted so that they may be plugged at the completion of the test program. In order to ensure that the correct tube is plugged, it is necessary that they be marked or otherwise identified visually so that workers may insert the applicable plugging device into the proper tube. It is very important that the inside of the heat exchanger tubes be kept free from contamination of any kind during the inspection and marking operations, as contamination of the inside of the tubes from any source, such as paint used to mark the tubes for plugging, would interfere with the seal of the plugging device used and, therefore, may result in a plugged tube which continues to leak and pose a safety hazard. At the present time, the only workable method for accomplishing the marking operation is for workers to enter the steam generator header compartments in order to identify and mark the defective tubes for later plugging. This marking operation constitutes a serious health hazard to the workers involved as the steam generator is generally contaminated with radioactive material.
In order to protect the health of the workers involved and to comply with the limitations imposed on personnel exposed to radiation as specified by the Nuclear Regulatory Commission, it is necessary that several individuals be employed to perform the marking operation. As many as eight or more workers may be required to complete the marking of defective tubes in a single steam generator. Each worker must be replaced once he has reached the maximum levels of radiation exposure specified by the Nuclear Regulatory Commission for a calendar quarter, and once he has reached this maximum level of exposure, he may not again be safely exposed to further radiation until the next calendar quarter. Thus, several "new" men who have never before performed the marking operation must be hired and trained for each overhaul and inspection. Hence, it may be seen that the performance of this tube marking operation unnecessarily hazards the health of workers performing the task and entails considerable expense to train personnel who are useful for only a limited time.
At present, there are no devices available to replace human workers in performing the marking function; however, there are available various apparati and systems capable of remotely examining steam generator tubes for existing or potential defects, thereby greatly reducing human contact with radioactive material during the testing process. It is clearly disadvantageous to use human workers to mark the defective tubes, due to the potential hazards to their health and the fact that once the workers have reached this maximum level of radiation exposure, they may no longer be used to perform the marking operation until the next calendar quarter.